The subject matter disclosed herein relates to the art of turbomachines and, more particularly, to a turbomachine having an inner-to-outer turbine casing seal assembly.
Many existing gas turbines include an annular inner casing mounted for radial and axial expansions and contractions relative to an annular outer casing. The annular inner casing is formed from two or more segments joined along bolted flange split lines. Other systems may employ a single piece annular inner casing. The annular outer casing is often formed by two generally semi-circular halves joined along a midline. The annular inner casing supports nozzles and shrouds for the turbine. The annular outer casing supports combustors as well as various ancillary components such as cooling circuits. Thus, the annular inner casing is exposed to a gas stream at a temperature higher than a gas stream passing through the annular outer casing. Exposure to gas streams at different temperatures leads to different expansion rates for each of the annular inner and outer casings.
Due to the different relative rates of expansion of the annular inner casing and annular outer casing, a seal assembly is generally required to reduce leakage. In many systems a series of leaf-type seals are arranged between the annular inner and annular outer casing. The leaf-type seals are arranged in an arcuate end-to-end relationship overlapping sealing areas on the annular inner and annular outer casings. The end-to-end relationship creates intersegment gaps that are configured to accommodate the relative axial expansions and contractions of the annular inner casing relative to the annular outer casing. A cover plate is often provided over the intersegment gaps to further reduce leakage.